Low-aberration high-speed-compatible optical delay lines and methods thereof

Abstract

An example architecture for providing a delay line for optical techniques. The delay line architecture includes a focusing element that has a focal axis disposed parallel to its length. The line of symmetry provided by the focal axis obviates path-length-dependent aberrations caused by the off-axis beam translations. The systems also provide varying geometries of movable mirrors, including a galvanometer mirror and a rotating polygonal mirror. The systems and methods also provide techniques for generating and detecting coherent Raman spectra using a picosecond probe pulse.

What is claimed is: 
     
       1. A delay module configured to delay a first light field to create a delayed light field comprising:
 a movable mirror, rotatable about an axis; 
 a focusing optical element having a focal axis parallel to the rotation axis of the movable mirror; and 
 a return mirror; 
 wherein the movable mirror is configured to:
 receive the first light field at a first light path and a first path length; 
 vary the first path length as the movable mirror rotates; and 
 reflect the first light field to the focusing optical element along a plane that does not include the first light path; 
 
 wherein the focusing optical element is configured to:
 receive the first light field reflected from the movable mirror; and 
 focus the first light field on the return mirror; 
 
 wherein the focal axis of the focusing optical element is perpendicular to a movement of the first light field so that the first light field remains focused on the return mirror with minimum aberration throughout a range of motion of the first light field; and 
 wherein the return mirror is configured to:
 receive the first light field reflected from the focusing optical element; and 
 reflect the first light field back to the focusing optical element and to the movable mirror along a second light path. 
 
 
     
     
       2. The delay module of  claim 1 , wherein the second light path is the same or substantially the same as the first light path. 
     
     
       3. A system comprising:
 the delay module of  claim 1 ; 
 a detector configured to combine a second light field with the delayed light field after the second light field interacts with an object of interest; and 
 a processor configured to calculate a complex refractive index of the object of interest based on optical interference between the delayed light field and the second light field after the second light field interacts with the object of interest. 
 
     
     
       4. The system of  claim 3  further comprising:
 a light field source configured to provide an input light field; and 
 a beam splitter configured to split the input light field into the first light field and the second light field; 
 wherein:
 the movable mirror is positioned such that the movable mirror intersects the focal axis of the focusing optical element; 
 the return mirror is positioned such that the return mirror intersects the focal axis of the focusing optical element; and 
 the first light field approaches the delay module along a path which is a linear combination of the axis of the movable mirror and the focal axis of the focusing optical element. 
 
 
     
     
       5. The system of  claim 3 , wherein the focusing optical element is a cylindrical mirror;
 wherein the movable mirror is selected from the group consisting of a planar galvanometer mirror and a polygonal mirror; and 
 the system has a scan rate of greater than 1.0 kHz. 
 
     
     
       6. The system of  claim 5  having a scan rate of greater than 40.0 kHz. 
     
     
       7. A method comprising:
 directing a first light field to the delay module of  claim 1  to create the delayed light field. 
 
     
     
       8. The method of  claim 7  further comprising:
 directing an input light field across a beam splitter such that the input light field is split into the first light field and a second light field; 
 combining a third light field with the second light field and the delayed light field to create combined light fields; 
 directing the combined light fields across an object of interest, thereby creating one or more new light fields with new spectral frequency content; 
 directing one or more of the new light fields onto one or more detectors after transmission through or scattering from the object of interest; and 
 determining a frequency-dependent phase and/or amplitude of one or more of the new light fields based on a delay between light fields of the combined light fields; 
 wherein the third light field is an optical pulse with spectral content of less than  30  wavenumbers and being fixed in time with the second light field; and 
 wherein either:
 the one or more new light fields are detected at higher optical frequencies than the third light field; or 
 the one or more new light fields are detected at lower optical frequencies than the third light field. 
 
 
     
     
       9. The method of  claim 8  further comprising calculating a complex refractive index of the object of interest based on optical interference between the delayed light field and the combined light fields after the combined light fields interact with the object of interest. 
     
     
       10. The method of  claim 8 , wherein:
 the first light field and the second light field are optical pulses with spectral content of greater than 200 wavenumbers; and either
 the one or more new light fields are detected at higher optical frequencies than the delayed light field and the second light field; or 
 
 the one or more new light fields are detected at lower optical frequencies than the delayed light field and the second light field. 
 
     
     
       11. The method of  claim 8  further comprising:
 combining another light field containing the same frequency components as the one or more new light fields; and 
 constituting a local oscillator with any of the light fields previous to detection. 
 
     
     
       12. The method of  claim 7  further comprising:
 directing an original light field across a first beam splitter such that the original light field is split into the first light field and a second light field; 
 directing the second light field across an object of interest, thereby creating a third light field having new spectral frequency components compared to the second light field; 
 collecting the third light field after the second light field scatters from the object of interest and/or after the second light field transmits through the object of interest; 
 directing the delayed light field into a material to generate a portion of the delayed light field having the same frequency components as the third light field; 
 combining the third light field with the portion of the delayed light field having the same frequency components as the third light field in a second beam splitter, thereby creating combined light fields; 
 directing the combined light fields onto one or more detectors; and 
 determining a frequency-dependent phase and/or amplitude of the combined light fields based on a delay between the delayed light field and the second light field. 
 
     
     
       13. A method comprising:
 directing a second light field to the delay module of  claim 1  to create the delayed light field. 
 
     
     
       14. The method of  claim 13  further comprising:
 directing an original light field across an object of interest, thereby creating a first light field with new spectral frequency content compared to the original light field; 
 collecting the first light field after it scatters from the object of interest or after it transmits through the object of interest; 
 directing the first light field across a first beam splitter such that the first light field is split into the second light field and a third light field; 
 combining the delayed light field and the third light field in a second beam splitter to create combined light fields; 
 directing the combined light fields onto one or more detectors; and 
 determining a frequency-dependent amplitude of the combined light fields based on a delay between the delayed light field and the third light field; 
 wherein the second light field and the third light field are separately and simultaneously detected at +45 degrees and at −45 degrees with respect to their primary polarization direction. 
 
     
     
       15. A method comprising:
 directing a third light field to the delay module of  claim 1  to create the delayed light field. 
 
     
     
       16. The method of  claim 15  further comprising:
 directing a first light field across an object of interest; 
 passing a second light field through a beam splitter to create the third light field; 
 directing the delayed light field across the object of interest; 
 directing a picosecond probe light field across the object of interest; 
 creating a signal field with the first light field, the delayed light field, and the picosecond probe light field after the first light field, the delayed light field, and the picosecond probe light field interact with the object of interest; and 
 analyzing the signal field with a broadband coherent anti-Stokes Raman scattering technique after applying delay on the delayed light field.